Gold nanoclusters-decorated graphitic carbon nitride nanocomposites with antibacterial and anti-biofilm activities

Gold nanoclusters (AuNCs) are of great potential in antibacterial field, but their unsatisfactory stability as a result of high surface free energy limited their practical applications. One efficient solution is loading the ultrasmall AuNCs onto a substrate or matrix. In this work, graphitic carbon nitride (CN) nanoparticles were firstly functionalized with imidazole groups via a photocatalytic reaction. Then, AuNCs were in-situ synthesized on surface of CN by using imidazole moieties as the reducing and stabilizing ligands via formation of Au-N bonds. Transmission electron microscopy (TEM) analysis of the obtained CN-AuNC nanocomposites verified the uniform distribution of AuNCs with mean size of 1.8 nm on CN surface. Since the coordination strength of Au-N bond is weaker than that of Au-S bond, ligand exchange can occur for the imidazole-protected AuNCs due to ligand exchange in the presence of thiol compounds. Accordingly, the obtained CN-AuNC nanocomposites exhibited thiol depletion ability. The slow release of AuNCs from the CN surface can enter into Escherichia coli (E. coli) due to their ultrasmall size, consume bio-thiols reducing species and increase the oxidative stress, which effectively killed the bacteria and inhibited subsequent biofilm formation. This paper provides a promising bactericidal nanocomposite with intrinsic properties for sterilization.